GB849184A - Isomerisation of paraffin hydrocarbons - Google Patents

Abstract

The isomerisation of normal pentane, hexane or heptane is effected at 600 DEG -1,000 DEG F. and 50-1,000 p.s.i.g. using a LHSV of 0,5-40 in the presence of 0,5-20 moles of hydrogen per mole of hydrocarbon over a catalyst comprising a mechanical mixture of particles of size less than 100 microns diameter of (1) an alumina carrier having 0,05-5% by weight of platinum deposited thereon forming 0,1-0,9 of the weight of the mixture and (2) a silica-alumina cracking component having CAT-A cracking activity of 20-50 and preferably having an alumina content of at least 8%, the catalyst mixture being such that it has a dehydrogenating activity of 20-2,000, measured in units of 10-6 mols/second per gram of catalyst of benzene formed on passing cyclohexane over the catalyst at 750 DEG F. and 350 p.s.i.g. at a LHSV of 5,000 with hydrogen in a molar ratio to cyclohexane of 4 : 1.ALSO:A hydrocarbon isomerisation catalyst comprises a mechanical mixture of particles of less than 100 microns in diameter of (1) an alumina carrier having 0.05-5% of platinum deposited thereon and forming 0.1-0.9 of the weight of the mixture and (2) a silica-alumina cracking component having a CAT-A cracking activity of 20-50, the mixture being such that it has a dehydrogenation activity of 20-2,000 expressed as the rate of formation of benzene in 10-6 moles/second per gram of catalyst on passing cyclohexane over the catalyst at 750 DEG F. and 350 p.s.i.g. and a LHSV of 5,000 in the presence of 4 moles of hydrogen per mole of cyclohexane. The alumina supporting the platinum may have a surface area of 10-500 square metres per gram and may be a precipitate or gel. Although it may contain eta, chi, gamma, theta, delta or alpha alumina it is preferably ordinary activated alumina obtained by controlled calcination of alpha alumina trihydrate containing chi and gamma forms. It preferably has a density of 0.2-2 grams/c.c. Eta alumina obtained by calcining beta alumina trihydrate can also be used. The platinum may be deposited by impregnation with an aqueous solution of chloroplatinic acid or its ammonium salt followed by drying and reduction. The silica-alumina may be a natural clay or a synthetic composite. The latter may be formed by cogellation by mixing an acidic aluminium salt solution with sodium silicate, drying and calcining at 900-1400 DEG F. or by mixing separately formed hydrogels e.g. by ball-milling or by precipitating alumina on a previously formed silica gel or by impregnation of a preformed silica gel with an aqueous aluminium salt followed by decomposition. The composite may also be formed in spheroids as in U.S.A. Specification 2,384,946 or by the process of U.S.A. Specification 2,469,314 to give a product of pore diameter 50-75 , a surface area of at least 400 square metres per gram a particle density of 0.71-0.95 gram/c.c. and an alumina content of 18-38%. In general the composite should have a surface area of at least 300 square metres per gram, a particle density below 1.2 gram/c.c. and an alumina content of at least 8%. If it is desired to have the final catalyst mixture in pellet or other compounded form, this is preferably effected before impregnation of the alumina with platinum to avoid damaging the platinum during burning of the binder. The two components of the catalyst may have different particle size to assist in separating if necessary.